The invention relates to endless power transmission belts, but more particularly, the invention relates to what some in industry term as "raw edge" belts where oppositely facing friction driving surfaces are formed of an elastomeric body and in which are dispersed transversely oriented fibrous members.
There are several belt configurations which have "raw edge" friction driving surfaces defined as part of a layer where discontinuous fiber is dispersed and transversely oriented in an elastomeric matrix. An example of a joined belt utilizing fiber dispersed in an elastomeric matrix is shown in U.S. Pat. No. 1,777,864.
An example of a "raw edge" V-Belt employing discontinuous fiber dispersed in an elastomeric matrix is shown in U.S. Pat. No. 3,416,383. The fiber is transversely oriented at angles varying from 90.degree..
Ribbed-belts also may have a "raw edge" construction and employ a layered construction with discontinuous fiber transversely oriented in an elastomeric matrix. U.S. Pat. No. 4,330,287 discloses such a construction.
All of the foregoing patents disclose a construction where generally the end portions of the dispersed fiber terminate or are severed at their oppositely facing friction driving surfaces; however, the '383 Patent further shows that portions of the "raw edge" may wear at a faster rate than embedded fabric layers but not faster than the surfaces where there is embedded fiber.
The friction characteristics of the driving surfaces for all of the described belts may be modified by a construction where there are discrete protrusions of fiber extending beyond an elastomeric portion of the driving surfaces. The file history of the U.S. Pat. No. 3,871,240 includes photomicrographs showing that end portions of fiber are exposed at oppositely facing frictional driving surfaces of the belt. As further explained in the '240 Patent, cord or fabric at concentrations of 20 percent by volume are preferred although concentration as low as 5 percent may be used. This Patent also teaches, that fiber, when loaded in an elastomer at the preferred concentrations, do not give the best results.
The preferred construction of U.S. Pat. No. 3,871,240 may not be a suitable solution for all belt types because of the relative height of the friction driving surfaces. For example, the use of cord or fabric is not a desirable solution for a multi-ribbed belt because of the relative small height of the ribs.
Another use of fiber at friction driving surfaces is shown in U.S. Pat. No. 3,190,137. Flocked fiber is embedded and vulcanized into peripheral sides of oppositely facing driving surfaces leaving very little, if any protruding fiber.